Adding an object before the current index in UICollectionView - ios

Question

I have a simple collection view that has two types of cells. A counter cell, and an "add" cell. My goal is to have the "add" cell remain at the end of the index after new objects are added. When I run the application my "add" cell appears but I get an error when the "add" button is pressed.
Here is the error:
Terminating app due to uncaught exception
'NSInternalInconsistencyException', reason: 'Invalid update: invalid
number of items in section 0. The number of items contained in an
existing section after the update (1) must be equal to the number of
items contained in that section before the update (1), plus or minus
the number of items inserted or deleted from that section (1 inserted,
0 deleted) and plus or minus the number of items moved into or out of
that section (0 moved in, 0 moved out).'
And here is my code:
// retrievedCounters is an NSMutableDictionary
- (NSInteger)numberOfSectionsInCollectionView: (UICollectionView *)collectionView {
// only want one section
return 1;
}
- (NSInteger)collectionView:(UICollectionView *)view numberOfItemsInSection:(NSInteger)section {
// get the current count and add one for the "add" cell
return retrievedCounters.count + 1;
}
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath {
UICollectionViewCell *cell;
// check whether the index path is at the very end and add the appropriate cell
if (indexPath.row == retrievedCounters.count) {
cell = [collectionView dequeueReusableCellWithReuseIdentifier:#"AddCounter" forIndexPath:indexPath];
}
else {
cell = [collectionView dequeueReusableCellWithReuseIdentifier:#"CounterCell" forIndexPath:indexPath];
}
return cell;
}
- (void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath
{
[collectionView deselectItemAtIndexPath:indexPath animated:YES];
// insert new counter at index path
[self.collectionView insertItemsAtIndexPaths:#[[NSIndexPath indexPathForItem:retrievedCounters.count-1 inSection:0]]];
}
Thank you to anyone who can help!

Answer 1

The error indicates a data source issue when changing your datasource. The number of your keys in the mutable dictionary is not correct.
Presumably you are using the NSIndexPaths as keys and the data you need as values. I would think it easier to use an array instead (indexPath.row would then simply point to the right object in the right order).
Check your update method where you change the data in the datasource. You should ensure that your dictionary contains the expected number of items.
In your error message, the 1 item before and after the insert seems to indicate that maybe your dictionary became nil and therefore returns a zero count. Ensure that you have a properly instantiated instance variable.

Answer 2

In your objects array whenever you add new objects
create new array for new objects and than add it like this
[existingArray addObjectsFromArray:newarray];
the sequence would be maintained